This invention describes a method to prepare chemically toner, wherein the particle size of the required toner is achieved by aggregation (flocculation), preferably using an acid for flocculation, which is unaffected by any temperature change. A desired particle size may be achieved during the flocculation process involving a latex, a pigment and a wax dispersion, using a required amount of acid. As the process is not sensitive to temperature, there is no further particle size growth, and also no loss in particle size during the fusing process. Toners prepared by this method exhibit good print quality.
One of the important requirements of laser printers is print quality. While there are several factors that affect print quality, one of the key factors is toner. In color laser printers, resolution is very critical. Higher or better resolution can be achieved by using small particle size toners. Small particle size toners are more difficult to achieve from a conventional toner processing technique, due to limitations in mechanical extruding/grinding. A more favorable way to achieve small particle size toner is to prepare the same through a chemical process.
There are at least two ways to prepare a chemical toner, suspension polymerization, or emulsion agglomeration (EA) processes. In an EA process, a latex is mixed or formed with a dispersion typically comprised of a pigment and wax, used either as individual dispersions or as a composite dispersion. The mixture is flocculated by addition of an inorganic salt, or an acid. The conversion of sub-micron particles of latex, pigment, and wax to micron(s) size aggregates is then increased by heating the mixture to a desired particle size.
To prevent any further growth of the toner particles, the pH is suitably adjusted to more alkaline conditions, and the particles are eventually heated at temperatures (above the softening temperature of the latex) to fuse and form a spherical or nearly spherical particle.
The spherical or non-spherical toner then can be mixed with extra particulate additives such as silica, titania, or other inorganic oxides to help in print quality or prevent the toner particles from sticking to each other.
This invention describes the use of a latex containing a long chain hydrocarbon such as a C12 chain (dodecyl, lauryl) monomer like lauryl methacrylate, to carry out the preparation of a chemical toner. The latex along with a pigment (cyan, magenta, yellow, etc) and wax (example polyethylene) on flocculation in the presence of a required amount of acid (example: nitric acid) can result in an aggregate whose size is easily adjusted by the amount of acid added. The aggregate is insensitive to temperature changes and on heating above the softening temperatures results in a generally round, but non-spherical particle.
The advantage of a non-spherical particle is the lower tendency of it to fuse or film in the developer nip, and the improved ease in cleaning off a photoconductor or photoreceptor member. This invention provides ease in manufacturability of the toner of desired size, since the tendency to increase in particle size is not dependent on temperature. Narrow particle size distributions are more readily achieved.
Lauryl methacrylate moieties in binder resins of dry toners are shown in U.S. Pat. No. 5,256,515 to Winnik et al. and U.S. Pat. No. 5,114,820 to Georges et al., and in UK Patent application 2 107 893 A by Kao Corporation. U.S. Patent Pub. No. 2004/0091809 by Qian et al. is illustrative of similar uses in liquid toners.
Toner manufactured by aggregations is exemplified by U.S. Pat. No. 4,983,488 to Tan et al, and U.S. Pat. No. 6,531,254 B1 to Bedells, as well as U.S. Patent Pub. No. 2004/0137348 A1 by Sun et al (assigned to the assignee of this invention).